It has been the object of many prior-art devices to detect the presence of air bubbles in an intravenous line. Such devices would normally set off an alarm to alert the appropriate medical personnel, who would then lightly rap the line to urge the bubbles up the line away from the patient. It is a tedious procedure to urge all the bubbles all the way up the IV line to the IV fluid reservoir. It is even more difficult to remove bubbles located downstream of a pump. Since, in an IV line that is not being pumped at high pressure, small bubbles usually do not pose much danger to the patient, busy medical personnel rarely go through the trouble of urging the bubbles all the way up the line. Consequently, the bubbles quickly move back down the line and are detected again, thereby setting off the alarm again. Thus, without an easy way of removing air from the IV line, the prior-art air-detection systems are more of a nuisance than an aid.
At least one medical apparatus in the prior art includes a line for recycling air removed from fluid back to a reservoir without opening the fluid flow loop to the environment. U.S. Pat. No. 4,874,359 to White et al. discloses a modular, power augmented medical infusion apparatus to provide rapid transfusion of relatively large quantities of blood, blood components, colloid and fluids to patients who require large quantities of these blood components to be rapidly transferred. The major components comprise a pair of filtered cardiotomy reservoirs, an air embolus sensor, a modular double roller pump, a heat exchanger, a bubble trap-filter and disposable fluid conduits. The bubble trap-filter is located in the distal most location of the recirculating loop just upstream of the Y-connector to the patient and the air sensor just downstream of the cardiotomy reservoir in the proximal location of the recirculating loop. Blood is circulated rapidly from the cardiotomy reservoir through the heat exchanger wherein it is heated or cooled as needed and through an air bubble trap filter having a nominal filtering capability of 33 microns. A secondary path from the filter is provided to permit the air trapped in the filter to be recycled to the reservoir without opening the infuser loop to the environment. The air bubble detection system uses an infra-red analyzer as a sensor. The detection system is configured to stop the pump and sound an audible alarm. It does not control the recycling of trapped air from the filter.
U.S. Pat. No. 4,764,166 to Spani discloses an ultrasonic device for detecting the presence of air in the fluid line of an IV infusion device comprises a transmitter and a receiver which are positioned to pinchingly engage a portion of the fluid line therebetween. Both the transmitter and receiver have convex-shaped lenses which contact and cause a slight indentation of the tube for enhanced coupling therebetween.
U.S. Pat. No. 4,734,269 to Clarke et al. discloses a venous reservoir bag with an integral high-efficiency bubble removal system. The system includes a container having an inlet for a fluid which includes liquid and gas bubbles, an outlet and upstream and downstream vents. A filter element is provided in the container between the inlet and the outlet. The filter element permits the passage of the liquid and inhibits the passage of the gas bubbles. The filter element is between the upstream and downstream vents so that gas bubbles can be vented through the upstream vent, and any gas bubbles downstream of the filter element can be vented through the downstream vent.
U.S. Pat. No. 4,661,097 to Fischell et al. discloses a method for removing gas bubbles from the fluid handling system of a medication infusion system implanted in a patient. Specifically, Fischell discloses a method for removing fluid and/or gas bubbles from a fluid reservoir and pumping chamber by applying a vacuum or negative pressure to the inlet filter, thereby drawing gas bubbles from the pumping chamber. The invention utilizes a fluid pump of a single valve positive displacement design with the pump chamber in fluid communication with the fluid reservoir.
None of the above references disclose a system that, on detection of air in the fluid, shuts off flow of the fluid to the patient and returns the fluid to an entry point in the system upstream of the pump.